2020-07-29_REVISION - M1977348 - Laserfiche WebLink

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' Amy Eschberger Project No 20144265 Colorado Division of Reclamation, Mining and Safety July 24,2020 2.3 Well Installation Consistent with MW-6 and MW-7, wells will be installed directly above the Niobrara-Codell contact. Since the ' contact will be encountered during drilling, the bottom of the borehole may need to be filled with bentonite. Coated bentonite pellets will be used and will be allowed to hydrate for a minimum of one hour prior to proceeding with the well installation. ' The wells will be constructed with 4-inch diameter, flush threaded, Schedule 80 PVC screen and riser pipe, such that they can be sampled for water quality. The screen in each well will be perforated with 0.010-inch slots and ' may be up to 20 feet in length. Final screen lengths will be determined in the field based on geology and actual groundwater conditions observed during drilling. PVC casing will be added to the top of the screen as it is lowered in the borehole until the screen reaches the desired depth and the casing extends 2 to 3 feet above the ground ' surface. The annular space around the screen and end cap will be backfilled with clean, washed, well-rounded silica sand (#10-20 or equivalent). The sand pack will be tremied from the bottom of the borehole to approximately 2 feet above the top perforation. A minimum of 2 feet of medium bentonite chips or coated bentonite pellets will be ' fed into the annular space above the screen and filter pack to provide a seal. Grout will be placed in the annular space above the bentonite seal to within approximately 3 feet of the ground surface. The grout will be mixed and placed in accordance with the State of Colorado Division of Water Resources (DWR)Water Well Construction ' Rules 2 CCR 402-2. Once the grout has cured, a protective steel casing will be placed around the PVC riser such that the bottom ' extends into the annual space to the top of the grout and the top rises above the PVC casing several inches. The protective casing will be equipped with a locking cover to prevent unauthorized entry and allow access for water level measurement. A concrete pad, approximately 3-foot square, sloping away from the well, will be constructed ' around the protective casing. 2.4 Surveying ' Surveying will be performed following well construction so that groundwater elevations can be established for monitoring flow directions and calculating hydraulic gradients. Surveying activities will be performed by a licensed surveying subcontractor to Golder and will be tied into the same coordinate system used for other surveying at the Site. ' 2.5 Well Development After the grout has set for a minimum of 48 hours and there has been sufficient time for the groundwater to enter the t well, the wells will be developed to improve water flow into the wells and reduce turbidity by removing fines from the screen and sand pack. Development will be conducted using a combination of surging and bailing/pumping and/or air lifting methods. During development, field parameters of pH, specific conductivity, and temperature will be ' measured after each casing volume removed. The wells will be developed until turbidity is reduced and field parameters have stabilized, or after five casing volumes have been removed, whichever comes first. In the event the well goes dry during purging, subsequent purging may be needed after the well is allowed to recharge. ' Equipment used for well development will either be new materials (such as tubing, surge blocks, pumps, inertial foot valves or disposable bailers) or will be decontaminated using a low phosphate soap (such as Alconox) ' solution followed by a distilled water rinse. It is assumed purge water will be non-hazardous and can be discharged onto the ground surface. 1 ' J GOLDER 3